The ADL-600 was designed by Anthony DeMaria with a no-holds-barred signal path.
The PreSonus ADL 600 is a high-voltage, 2-channel microphone preamp designed by world-renowned analog
tube circuit designer Anthony DeMaria. It utilizes a Class A discrete design with 3 vacuum tubes per channel for maximum headroom
Control and Flexibility
The ADL 600 is designed for supreme sonic performance and flexibility with XLR microphone/line inputs and 1/4" instrument
inputs. The input selector allows for selection between Hi-Z instrument input, line input, and 4 different mic impedances
for a number of applications. The rotary High Pass Filter switch has 3 settings (40Hz, 80Hz, and 120Hz @ 6dB per octave) for
controlling room rumble and low-frequency noise. The input gain attenuator delivers 5dB-step increments and a total gain of
over 72dB. The output stage is controlled by a variable conductive plastic attenuator that delivers +/-10dB of fine tune trim
adjustment to dial-in the perfect gain structure for the application at hand. The ADL 600 also includes 48V phantom power
and a -20dB pad.
Under the Hood
There are no op-amps or integrated circuits (IC's) in the signal path to ensure the purest sound possible. The dual-transformer
design guarantees ultralow-noise operation with maximum common mode rejection.
The ADL 600 is loaded with both fast-acting 8-segment LED meters for accurately detecting fast transients and peaks, as well
as large analog VU meters for metering output level.
The overall approach to the ADL 600's design was to keep the signal path as simple as possible by keeping the component count
to a minimum. The few components that are in the signal path were chosen for their sonic qualities: custom audio transformers,
polyfilm pulse capacitors, 1% metal film resistors, and conductive plastic potentiometers. Also, rotary switches and fixed
1% metal film resistors are used in the preamp gain circuit to keep noise to a minimum and to prevent any coloration that
may be caused by a potentiometer.
The custom-designed input transformer is fully encased in a Mumetal enclosure, yielding
excellent noise characteristics and magnetic shielding. The transformer interfaces the balanced mic/line inputs to the tube
preamp circuits. On the primary side of the transformer are circuits for +48V phantom power, microphone impedance, 20dB pad,
and line input. All of these are switched by sealed relays for reliability. Also, the relays are located at the point where
the switching is required. This minimizes the signal path length and helps to keep noise low.
The combination of a
12AT7A tube and a 6922 tube form the principle gain stage, giving the ADL 600 its open and airy sound. This is primarily due
to the circuit topology and the wide power supply rails applied to this stage-+/-320VDC. A high endurance Grayhill rotary
switch and 1% metal film resistors are used to set the gain in 5dB steps. Polyfilm pulse capacitors are used for interstage
coupling to maintain stunning clarity. The preamp stage drives the High Pass filter circuit and the Output trim. The High
Pass filter can be bypassed or set to 40Hz, 80Hz, or 120Hz. Polyfilm capacitors are used for the filters, which are first-order
and provide 6dB/octave roll-off. The Output trim potentiometer feeds the input to the second 6922 tube, which drives the Mumetal
shielded output transformer. A DPDT relay allows for output phase reversal at the primary side of the output transformer.
PreSonus ADL 600 Stereo High Voltage Tube Microphone Preamp Features:
- High-voltage Class A dual-transformer design
- >73dB gain
- Selectable microphone input impedance
- Switched gain and variable fine trim controls
- Microphone (XLR), instrument (1/4"), and line (XLR) inputs
- Ultralow noise (-100dB S/N ratio)
- Variable high-pass filter, 48V, -20dB pad, polarity invert
- Analog VU and fast-acting LED metering
Make your mixes richer than ever. Order the ADL 600 today!
PreSonus ADL 600 Stereo High Voltage Tube Microphone Preamp Specifications:
- Input impedence:
- Microphone: Selectable, 150/300/900/1500 ohm
- Balanced line: 2k ohm
- Instrument: 100k ohm
Maximum input level:
- Microphone (1500 ohm, +20dB pad out): +5dBu
- Microphone (1500 ohm, +20dB pad in): +25dBu
- Balanced line: +30dBu
- Instrument: +30dBu
- Microphone (1500 ohm, +20dB pad out): +5dBu
- Balanced line: -12dB to 40dB
- Instrument: -5dB to 42dB
- Noise floor (all inputs, minimum gain): -95dBu (A-weighted)
- Microphone equivalent input noise (EIN): -125dBu (A-weighted)
- Frequency response: 10Hz to 45kHz ±1dB
- Maximum output level: +23dBu @ 0.5% THD+N
- Output impedance: 600 ohm
- Tube complement (per channel): 1 - 12AT7A, 2 - 6922
- Power (factory-configured): 115 or 230V AC/100 watts
- Dimensions: 19"W x 3-1/2"H x 17"D
- Weight: 28 lbs.